The present invention relates to improvements in railroad tank cars, and in particular to such a car with reduced car weight, and having integrated and unified load-bearing structures so that dynamic train loads and static loads are shared between the tank itself and the underframe portion of the structure of the tank car.
Many railway tank cars have completely separate underframes with tank support structures mounted on the underframes and tank bodies attached to the support structures. While such cars have ample strength it is desired to provide tank cars of lighter weight, since a car whose tare weight is less can carry greater weights of cargo and thus generate greater amounts of revenue using a given amount of fuel.
A type of tank car structure used extensively in North America has a stub sill supported by a wheeled truck attached to each end of a tank. The structure of the tank supports itself between the stub sills, carrying not only the static and dynamic loads resulting from the weight and movement of liquid cargo contained in the tank, but also dynamic loads resulting from operation of the car as part of a train. In such cars forces are concentrated in and carried through the locations where the stub sills are attached to the tank. As a result, such cars all too frequently are subject to structural failure during train operation.
A type of tank car structure used widely on European railroads utilizes a relatively heavy underframe including a substantial longitudinal frame structure upon which are carried saddles to support a tank. Cargo loads are transferred to the underframe of such a car by the saddle structures alone, and a relatively massive center sill structure, separate from the tank, is utilized to carry most dynamic train loads. Such cars are significantly heavier than is desired, for a given liquid cargo weight capacity.
Another result of such a structural design is that the end portions of the underframe of such a car have to be of relatively heavy construction in order to permit the car when loaded to be supported on jacks located at the corners of the underframe, since there is a relatively long lever arm between the corners of the underframe and the saddle attachment locations, where the weight of the tank and included cargo is transferred to the underframe.
A further deficiency of such a railroad tank car design is that the structures of the tanks and the underframes of the cars do not cooperate with each other to carry dynamic loads during operation of such cars as part of a train.
What is needed, then, is an improved railroad tank car of reliably durable construction but lighter in weight than previously known cars. Additionally, it is desired for such a car to be able to be assembled with a minimum of special skill requirements and a minimum of requirements for formed metal parts included in such a car""s structure.
The present invention provides a railroad tank car structure which answers the aforementioned need for a tank car of ample strength and durability combined with lighter car weight and simple construction, by providing a car in which the tank shell and underframe components are better integrated into a unified, strong, and light structure than has previously been accomplished.
In one preferred embodiment of the present invention a railroad tank car includes a pair of transversely extending saddle bolsters interconnected by a center sill structure, and a stub sill extends outward longitudinally from each saddle bolster. A tank is closely supported by the saddles of the saddle bolsters. The tank also rests atop and is fastened, preferably welded, to the center sill and to each stub sill, so that the stub sills, saddles, tank, and center sill are a unified structure and cooperate closely to carry the static loads imposed by the weight of cargo carried in the tank and the dynamic loads that result from operation of a train including such a car and its cargo.
In one embodiment of the present invention each saddle is connected with the tank over a significant portion of the outside of the tank and provides support for the tank against atomospheric xe2x80x9cvacuum pressurexe2x80x9d in the case of improper venting of the tank during discharge.
In one preferred embodiment of the present invention the interconnection of the tank with the stub sills, saddle bolsters, and center sill includes the use of doubler plates that carry and distribute forces among the various portions of the tank car through structure of great enough size that critical force concentrations are avoided, while the car""s weight is reduced.
In a preferred embodiment of the invention doubler plates are designed to function as linear stiffeners in transition zones between joints.
In one embodiment of the invention stub sills, saddle bolsters, and a center sill are constructed primarily by welding flat steel plate parts so that construction of such a car is uncomplicated.
In one embodiment of the present invention the stub sills include torsion box structures interconnecting the bottom plate and top shear plate of the stub sill and providing ample stiffness in the stub sill.
In one embodiment of the invention a portion of the tank located longitudinally outward from the saddle bolsters rests atop and is fastened to the top shear plate of the stub sill.
In a preferred embodiment of the invention, each stub sill includes a coupler tube capable of accepting either European hook-and-link couplers or North American type automatic knuckle couplers and associated cushioning devices.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention, taken in conjunction with the accompanying drawings.